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• USDA FOREST SERVICE RESEARCH NOTE

PNW-321 October 1978

EFFECTIVENESS OF THREE INSECTICIDES APPLIED AT TWO DROPLET SIZES
FOR CONTROL OF THE DOUGLAS-FIR TUSSOCK MOTH
^VUs\ AND WESTERN SPRUCE BUDWORM

r

•3

by

1 2 , y 3

George P. Markin, Harold 0. Batzer. and J. Wayne Brewer

ABSTEACT

Carbaryl, trichlorfon, and acephate were evaluated
at two different droplet sizes against laboratory raised
Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough) ,
and field populations of the western spruce budworm,
Choristoneura occidentalis Freeman. Small droplets of
carbaryl and trichlorfon caused higher mortality of both
Douglas- fir tussock moth and western spruce budworm than
did larger droplets. Small droplets of acephate gave a
higher mortality of the western spruce budworm in the
field but were less effective against the Douglas-fir
tussock moth in laboratory bioassays.

USDA Forest Service, Pacific Southwest Forest and Range Experiment
Station, Davis, Calif. 95616.
2

USDA Forest Service, North Central Forest Experiment Station, St. Paul,
Minn. 55108.

"^Department of Zoology and Entomology, Colorado State University,
Ft. Collins, Colo. 80523.

REST SERVICE - U.S. DEPARTMENT OF AGRICULTURE - PORTLAND, OREGON

INTRODUCTION

In the western United States, two
major forest defoliators are the Douglas-
fir tussock moth, Ovgyia pseudotsugata^
(McDunnough) , (Wickman 1963, Wickman
et al. 1973) and the western spruce
budworm, Chovistoneura occidentalism
Freeman (Carolin and Honing 1972) .
Before 1973, the only extensively used
control for these two pests was aerial
applications of DDT. The U.S. Forest
Service has undertaken an extensive
research program to find alternate
chemical insecticides. By 1975,
field tests had indicated that three
chemicals, carbaryl (SEVIN® 4 Oil) ,6
trichlorfon (Dylox®1.5 oil), and
acephate (Orthene® 75S) were promising.

All earlier tests used boom-
mounted conventional hydraulic pressure
nozzles, and the question was raised
as to whether other commerically
available spray systems could ef-
fectively apply these materials. We
were particularly interested in
rotary atomizer systems, which are
reported to increase the total number
of droplets per given volume of spray,
thus increasing their coverage of
the treated area and their chance of
contacting the target insect.

A series of tests was conducted
in 1975 with the aforementioned
insecticides, to compare a rotary
atomizer system that produces a

Lepidoptera : Lymantriidae .

^Lepidoptera: Tortricidae.

6

The use of trade, firm, or
corporation names in this publication
is for the information and convenience
of the reader. Such use does not
constitute an official endorsement or
approval by the U.S. Department of
Agriculture of any product or service
to the exclusion of others which may
be suitable.

small droplet with a conventional
hydraulic system that applies larger
droplets for control of both the
Douglas- fir tussock moth and the
western spruce budworm.

MATERIALS AND METHODS

The spray plots were located in
the Wenatchee National Forest on the
east side of the Cascade Range ap-
proximately 32 km northwest of
Ellensburg, Washington. Laboratory
facilities for conducting the bioassay
were at the Department of Biology,
Central Washington State College at
Ellensburg. Plots in a fir forest
that contained an outbreak of budworm
were treated, and population reduction
was conventionally evaluated. Also,
foliage samples were collected after
treatment and brought into a laboratory
where they were bioassayed by using
laboratory reared tussock moth. A
bioassay was necessary because, in
1975, no suitable outbreak populations
of tussock moth existed.

Twenty-one rectangular plots,
each about 6.5 ha in size and
separated from each other by a
minimum of 1 km, were selected for
the test. In the center 1 ha of each
plot, 15 open-grown trees, both
Douglas-fir, Pseudotsuga menziesii
var. glauca (Beissn.) Franco, and
grand fir, Abies grandis (Dougl.)
Lindl . , 9 to 18 m high were selected
as sample trees.

Three of the 21 plots were ran-
domly selected as untreated controls;
the remaining plots were divided into
three replicates of 6 plots, each at
about the same elevation, giving a
randomized block design. The assigning
of a treatment to the six plots in each
replicate was random. Treatment was
made when 90 percent of the bud caps
had fallen from the new growth of
Douglas- fir.

2

A Hiller 12E helicopter was used
for applying all materials. Standard
size spray droplets (referred to as
large droplets) were applied with a
9.14-m boom equipped with Spraying
Systems (Wheaton, 111.) T8002 flat-
fan nozzle tips. The small droplet
size was obtained with five to eight
spinning disc atomizers on a 5.49-m
support boom. The atomizers were
basically the modified version of
the Bals Turbair spinning nozzle
described by Boving et al. (1971).

Carbaryl (diluted 1:1 with
diesel oil) was applied at the rate
of 2.24 kg AI/9.35 liters per ha
(2 lb Al/gal per acre) . Trichlorfon
was applied undiluted at 1.68 kg Al/ha
(1.5 lb Al/acre) . Acephate was
applied at 1.12 kg AI/18.7 liters
per ha (1 lb AI/2 gal per acre) in
water. In mixing each of the
formulations , 0.1 percent Rhodamine B
dye was added to the finished spray
solution to facilitate spray deposit
assessment. The dye was first
dissolved in oleic acid (2.5 percent
of final spray solution) before
mixing with trichlorfon and carbaryl.

Spray deposit was sampled from
two aluminum plates and one white
Kromekote card placed in an open
area adjacent to each sample tree.
The amount of spray deposit was
determined by fluorescent methods
(Yates and Akesson 1963) . Deposit
on the plates was converted to liters
per hectare. The cards were used to
determine volume median diameter
(vmd) 7 and drop density with a
Quantimet 720 (Imanco Image Analyzing
Computer and Co., Monsey, N.Y.) ,
which electronically counted and sized
all spots formed by droplets larger
than 20 pm.

Volume median diameter (vmd) is
the droplet diameter satisfying the
requirement that half of the volume of
liquid is in droplets smaller and half
is in droplets larger than the vmd.

Samples to be used for bioassay
with tussock moth were collected 24 h
before treatment and at 30 min (carbaryl
and trichlorfon) or 24 h (acephate)
after treatment. Three branch tips
30 to 40 cm long were collected from
the midcrown of each tree; they were
placed in a perforated plastic sack,
the sack sealed around the stems, and
the base of the branches placed in
water. Ten third- instar, laboratory-
reared tussock moths were introduced
into each sack and allowed to feed for
7 days, after which the number of dead
and living larvae was counted to deter-
mine percent mortality.

The sample procedure for the
budworm was basically that described
by Carolin and Coulter (1972) ; it
consisted of counting the number of
larvae and buds on two 40-cm branches
removed from midcrown of each sample
tree at prespray (24 h) sampling and
four branches at three postspray
sampling intervals (3, 7, and 14 days) .
The population was expressed as the
number of budworm larvae per 100 buds.

Applications began on June 15
and were completed by June 19, 1975.
Temperatures ranged from 0° to 17 °C.
Windspeeds were below 8 km/h and
averaged 1-3 km/h. Two short rain
showers late in the afternoons of
June 18 (0.8 cm) and June 19 (0.5 cm)
occurred 7 to 10 h after the applications
had been made on the morning of those
days. No detectable rainfall occurred
during the remaining weeks of the study.

RESULTS

Table 1 shows the analysis of
spray deposit that reached the cards
and plates. The Bals Turbair type
spinning nozzle was found capable of
applying all three insecticides and
produced droplets with smaller vmd's
than the conventional spray system. It
also increased the number of droplets
recovered per unit of area. If we use
the vmd as an average droplet size to
determine the volume for that diameter

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droplet, the small droplets of carbaryl
were 26 percent of the volume of the
large droplets, trichlorfon 23 percent,
and acephate 50 percent.

Douglas-fir Tussock Moth

Large droplets of carbaryl gave
a mean mortality of 86.8 percent and
small droplets, 98.5 percent. This
difference was not statistically
significant (P = 0.05) .

The large droplets of trichlorfon
produced 66.3 percent mean mortality.
When droplet size was reduced, a sixfold
increase occurred in the number of
droplets recovered, and the mean mor-
tality increased to 90.2 percent, a
statistically significant difference
(P = 0.05) .

Although the two spray systems
satisfactorily atomized the oil-based
trichlorfon and carbaryl, giving
droplets with a fourfold difference
in volume, the same systems used with
the water-based acephate produced
droplets with only a twofold dif-
ference in volume.

The mean mortality obtained from
the bioassay of acephate was poorer
than expected. Neisess et al. (1976) ,
using a droplet of 5 3 3- urn vmd, pro-
duced a mean mortality of 97 and
98 percent with a 303-ym vmd droplet.
In comparison with these two tests,
both sizes of droplets produced less
mortality, possibly because much of
the mortality of acephate comes from
initial contact of the droplets on
the target insects, which our bioassay
did not measure.

Western Spruce Budworm

Table 1 shows effectiveness of
the two droplet sizes in reducing
natural populations of the western
spruce budworm. No significant dif-
ference (P = 0.05) occurred between
small and large droplets for carbaryl

or acephate at any of the three sample
intervals. As with the tussock moth,
trichlorfon produced the only statis-
tically significant change in mortality,
increasing the population reduction
from 63.1 to 96.2 percent (P = 0.05) .

DISCUSSION

This study demonstrated that other
spray systems besides conventional
hydraulic pressure nozzles are capable
of applying the three candidate in-
secticides for control of two important
defoliators of western forests. The
Bals Turbair type system effectively
reduced the vmd for all three materials
with corresponding increase in number of
droplets recovered at the sampling sites.
Use of smaller droplets did not decrease
the volume of the spray recovered with
the oil-based carbaryl and trichlorfon.
The volume of acephate recovered at
ground level, however, was less for
the smaller droplets than with the
large droplets. Future tests with
acephate using smaller droplets should
take into consideration the possibility
of loss by evaporation in the drier
climates of the West and the use of
antievaporants .

LITERATURE CITED

Boving, P. A., B. Maksymiuk, R. G.
Winter f eld, and R. D. Orchard.

1971. Equipment needs for aerial
application of microbial in-
secticides. Trans. Am. Soc.
Aeronaut. Eng. 14:48-51.

Carolin, V. M. , and W. K. Coulter.

1972. Sampling population of
western spruce budworm and
predicting defoliation on
Douglas-fir in Eastern Oregon.
USDA For. Serv. Res. Pap. PNW-149.
38 p. Pac. Northwest For. and
Range Exp. Stn. , Portland, Oreg.

5

Carolin, V. M. , and F. W. Honing.
1972. Western spruce budworm.

USDA For. Serv. For. Pest Leafl. 53.
8 p.

Neisess, J., G. P. Markin, and

R. Schaefer.

1976. Field evaluation of acephate
and dimilin against the Douglas-
fir tussock moth. J. Econ.
Entomol. 69:783-6.

Wickman, B. E.

1963. Mortality and growth

reduction of white fir following
defoliation by the Douglas-fir
tussock moth. USDA For. Serv.

Res. Pap. PSW-7. 15 p. Pac.
Southwest For. and Range. Exp.
Stn. , Berkeley, Calif.

Wickman, B. E. , G. C. Trostle, and
P. E. Buffam.

1973. Douglas-fir tussock moth.

USDA For.' Serv. For. Pest.

Leafl. 86. 6 p.

Yates, W. E. , and N. B. Akesson.
1963. Fluorescent tracers for
quantitative microresidue
analysis. Trans. Am. Soc.
Aeronaut. Eng. 6:104-7,
114.

Acknowledgments

We express our appreciation to the Department of Biology
at Central Washington State College, Ellensburg, for help in
providing laboratory space and equipment, and particularly for
help in hiring and directing the summer field crew. Part of
the funding for this study was supplied by the USDA Expanded
Douglas-fir Tussock Moth Research and Development Program,
K. H. Wright, Director, Portland, Greg.

6

GPO 987-0 1 5

t

This publication reports research involving pesticides. It does not contain
recommendations for their use, nor does it imply that the uses discussed
here have been registered. All uses of pesticides must be registered by
appropriate State and/or Federal agencies before they can be recommended.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable
plants, and fish or other wildlife — if they are not handled or applied properly.
Use all pesticides selectively and carefully. Follow recommended practices
for the disposal of surplus pesticides and pesticide containers.

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U S. DEPARTMENT 0' AGIICUETUIE

7

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